Optical imaging modules and optical detection modules including a time-of-flight sensor

ABSTRACT

The present disclosure describes optical imaging and optical detection modules that include sensors such as time-of-flight (TOF) sensors. Various implementations are described that, in some instances, can help reduce the amount of optical cross-talk between active detection pixels and reference pixels and/or can facilitate the ability of the sensor to determine an accurate phase difference to be used, for example, in distance calculations.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of priority of the following U.S.Provisional Patent Application Ser. Nos. 61/953,089 filed on Mar. 14,2014; Ser. No. 61/981,235 filed on Apr. 18, 2014; and Ser. No.61/987,045 filed on May 1, 2014. The contents of the prior applicationsare incorporated herein by reference.

BACKGROUND

Some handheld computing devices such as smart phones can provide avariety of different optical functions such as one-dimensional (1D) orthree-dimensional (3D) gesture detection, 3D imaging, proximitydetection, ambient light sensing, and/or front-facing two-dimensional(2D) camera imaging.

TOF-based systems, for example, can provide depth and/or distanceinformation. In general, TOF systems are based on the phase-measurementtechnique of emitted intensity-modulated light, which is reflected by ascene. The reflected light is imaged onto a sensor, and thephoto-generated electrons are demodulated in the sensor. Based on thephase information, the distance to a point in the scene for each pixelis determined by processing circuitry associated with the sensor.

Additionally, TOF-based systems can provide depth and/or distanceinformation via a pulse-measurement technique. The pulse-measurementtechnique employs an emitter and sensor as above; however, distance isdetermined by tallying the time for emitted light to reflect back ontothe sensor.

Integrating TOF sensors into devices such as smart phones, tablets orother handheld devices, however, can be challenging for several reasons.First, space in the host device typically is at premium. Thus, there isa need to achieve accurate TOF sensors having a relatively small height.Second, the size of the dies impacts production costs. Accordingly, itis desirable to achieve TOF sensors having a relatively small footprint.

While the foregoing issues also may be applicable to other types ofoptical imaging or detection sensors, another potential problem is morespecific to TOF sensors. In particular, the distance measurementsobtained by the pixels should be robust against phase delays caused, forexample, by thermal drifting effects. To address such concerns, in someTOF chips, a self-calibration of the TOF distance measurement isachieved by providing reference pixels that measure light from theillumination source. The use of such reference pixels necessitatesdirecting some of the light from the illumination source to thereference pixels, which may need to be separated optically from theactive pixels used to measure the distance to the scene.

TOF-based distance measurements via the pulsed-measurement techniqueshould be robust against thermal drifting effects. For example, in someinstances the precise time for commencement of the initial emission oflight from the emitter may be obscured by thermal drifting effects.

SUMMARY

The present disclosure describes optical imaging and optical detectionmodules that include sensors such as time-of-flight (TOF) sensors.

Various implementations are described that, in some instances, can helpreduce the amount of optical cross-talk between the active detectionpixels and the reference pixels and/or can facilitate the ability of thesensor to determine an accurate phase difference to be used, forexample, in distance calculations.

In one aspect, this disclosure describes an optoelectronic module thatincludes an illumination source, a sensor including spatiallydistributed detection pixels and at least one reference pixel, an opticsmember disposed over the illumination source and the sensor, and a lightbarrier separating an emission chamber of the module from a detectionchamber of the module. The optics member has a first transmissive regionover the illumination source and a second transmissive region over thedetection pixels. The illumination source and the at least one referencepixel are in the emission chamber, whereas the detection pixels are inthe detection chamber. Also, optoelectronic module includes at least oneof: (i) a partially reflective coating on a surface of the firsttransmissive region over the illumination source or (ii) a reflectivecoating on a surface of the emission chamber, wherein the coating isarranged such that some light from the illumination source is reflectedby the coating toward the at least one reference pixel.

In another aspect, an optoelectronic module includes a coating on asurface of the optic member's transmissive region over the illuminationsource, wherein the coating is at least one of an optical filtercoating, a partially-reflective coating, an anti-reflective coating or anon-transmissive coating.

In yet another aspect, an optoelectronic module includes one or moremicro lenses disposed over the detection pixels and/or the referencepixel(s).

According to a further aspect, each of one or more detection and/orreference pixels is at least partially surrounded laterally by a shieldof one or more layers that narrow an effective field of view for thepixel.

In accordance with another aspect, an optoelectronic module includes aprinted circuit board, and an illumination source mounted on or in theprinted circuit board. The module further includes spatially distributeddetection pixels and at least one reference pixel implemented in one ormore semiconductor sensor that are embedded within the printed circuitboard.

A further aspect describes a method of determining a distance to anobject using a time-of-flight sensor that includes active demodulationdetection pixels and one or more reference pixels. The method includesintegrating the active demodulation detection pixels during a firstintegration period and integrating the one or more reference pixelsduring a second integration period different from the first integrationperiod. Signals are read out from the active demodulation detectionpixels during a first read-out period after the first integrationperiod, and signals are read out from the one or more reference pixelsduring a second read-out period after the second integration period.

As described in accordance with another aspect, an optoelectronic moduleincludes control logic configured to tune an integration time of at thereference pixel(s).

Another aspect relates to a method of determining a distance to anobject using a time-of-flight sensor module that includes demodulationdetection pixels and one or more reference pixels. The method includesmeasuring sensed values from a particular demodulation detection pixeland from a particular reference pixel, and determining a phasedifference based, at least in part, on the sensed values and based onstored sensitivity values, wherein the sensitivity values are indicativeof amounts of optical cross-talk between the particular demodulationdetection pixel and the particular reference pixel. The module caninclude processing logic to implement the method.

In yet another aspect, an optoelectronic module includes a transmissivemember disposed over the illumination source and the sensor. Arespective black chrome coating is on opposite surfaces of thetransmissive member, wherein each of the black chrome coatings defines atransmissive window that allows light from the illumination source topass through to outside the module. Openings are provided in a portionof the black chrome coating on a sensor-side of the transmissive memberin a vicinity of the at least one reference pixel. In some cases, thepresence of the black chrome coating can enhance the amount of lightreflected to the reference pixels; providing part of the black chromecoating as a pattern can be used to prevent an excessive amount of lightfrom being incident on the reference pixels.

Other aspects, features and advantages will be readily apparent from thefollowing detailed description, the accompanying drawings, and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates general operation of a TOF camera system.

FIG. 2 illustrates an example of an optoelectronic module according tosome implementations of the invention.

FIG. 3 illustrates another example of an optoelectronic module accordingto some implementations of the invention.

FIG. 4 illustrates a further example of an optoelectronic moduleaccording to some implementations of the invention.

FIGS. 5-7 illustrated additional examples of optoelectronic modulesaccording to some implementations of the invention.

FIGS. 8A-8D illustrate examples of integration timing diagrams.

FIG. 9 is a flow chart of a method for determining a phase difference insome implementations of the invention.

FIG. 10 is a vector graph illustrating vectors to assist inunderstanding the method of FIG. 9.

FIG. 11 illustrates another example of an optoelectronic moduleaccording to some implementations of the invention.

DETAILED DESCRIPTION

As shown in FIG. 1, a TOF camera system 20 includes an illuminationsource 22. Modulated emitted illumination light 24 from the source 22 isdirected toward a scene 26 that includes one or more objects. A fractionof the total optical power directed to the scene is reflected back tothe camera 20, through optics 28, and is detected by a 3D imaging sensor30. The sensor 30 includes a 2D pixel matrix 32 of demodulation pixels34. Each pixel 34 is capable of demodulating the impinging light signal25 that is collected by the optics 28 (e.g., a lens) and imaged onto theimaging sensor 30. An electronics control unit 36 controls the timing ofthe illumination module 22 and sensor 30 to enable its synchronousdetection.

The demodulation values allow for each pixel 34 to compute thetime-of-flight, which, in turn, directly corresponds to the distanceinformation (R) of the corresponding point in the scene 26. The 2D grayscale image with the distance information can be converted into a 3Dimage at the data output interface 38 that includes an image processorand/or other control and processing logic (e.g., microprocessor and/orother circuitry). The 3D image can be displayed to a user, for example,on a display 40 or can be used as machine vision input.

The time-of-flight (TOF) is obtained by demodulating the light signalsreflected from the scene 26 and that impinge on the active pixels 34 ofthe sensor 30. Different modulation techniques are known, for examplepseudo-noise modulation, pulse modulation and continuous modulation. Thedistance to the object for each pixel then can be calculated based onthe detected signals using known techniques.

The sensor 30 can be implemented, for example as an integratedsemiconductor chip that also includes a region (e.g., a row) ofreference pixels 44. During operation, a fraction of the light from theforward path of the illumination source 22 is fed back to one or morereference pixels 44. The signals detected by the reference pixels 44 canbe used to re-calculate a zero-distance with every frame, therebyfacilitating self-calibration of the TOF distance measurement. Thesensor chip also can include, for example, control logic, decoder logicand read-out logic.

FIG. 2 illustrates an example of an optoelectronic module 100 thatincludes a light emission channel 102 and a light detection channel 104.A light emitter chip 106 and a TOF sensor chip 108 are mounted on afirst side of a printed circuit board (PCB) 110. The light emitter 106is an example of an illumination source. In some cases, the lightemitter 106 is operable to generate coherent, directional, spectrallydefined light emission. Examples of the light emitter 106 are a laserdiode or a vertical cavity surface emitting laser (VCSEL).

An optics member 116 spans across the channels 102, 104 and includestransmissive windows 122A, 122B that are substantially transparent to awavelength of light (e.g., infra-red radiation) emitted by the emitter106. In some instances, as shown in FIG. 2, the emitter and detectorwindows 122A, 122B are separated from one another by an opaque orsubstantially non-transmissive region 131 that forms part of the opticsmember 116. Light from the emitter 106 is directed out of the modulethrough the emitter window 122A and, if reflected by an object backtoward the module's detection channel 104, can be sensed by the TOFsensor 108.

The TOF sensor 108 can include an array of spatially distributed lightsensitive elements (e.g., active demodulation detection pixels) 124 aswell as one or more light sensitive reference pixels 128. Both thedetection pixels 124 and the reference pixels 128 are able to senselight at a wavelength emitted by the emitter 106. The detection pixels124 provide the primary signals for determining the distance to anobject outside the module. Signals from the reference pixels 128 can beused to compensate for drift and/or to provide a zero distancemeasurement. The sensor 108 can be implemented, for example, usingcharge-coupled device (CCD) or complementary metal oxide semiconductor(CMOS) technologies. In some cases, the reference pixels 128 are locatedon the same sensor chip as the detection pixels 124, although in othercases, as discussed below, they may be located on different chips. Insome instances, there may be an array of reference pixels (e.g., asingle line of pixels or multiple lines of pixels). Typically, there aremany fewer reference pixels 128 than detection pixels 124.

The emitter 106 and the TOF sensor 108 can be connected electrically tothe PCB 110, for example, by conductive pads or wire bonds. The PCB 110,in turn, can be connected electrically to other components within a hostdevice (e.g., a smart phone or tablet).

In the example of FIG. 2, a vertical shield (i.e., light barrier) 130extends between the optics member 116 and the surface of the TOF sensor108. The shield 130, which substantially attenuates the light or isnon-transparent (i.e., opaque) to the light emitted by the emitter 106,is disposed such that detection pixels 124 are located to one side ofthe shield and the reference pixels are located to the other side of theshield. The reference pixels 128 are thus disposed in the emissionchamber 102 on the same side of the shield 130 as the emitter 106. Thedetection pixels 124, however, are disposed on the other side of theshield 130 in the detection chamber 104. This arrangement allows a smallamount of light from the emitter 106 to be reflected by the transmissivewindow 122A for sensing by the reference pixels 128 without introducingoptical cross-talk from the emission chamber 102 to the detection pixels124.

In the illustrated example of FIG. 2, the non-transmissive section 131of the optics member 116 between the transmissive windows 122A, 122B canbe composed of the same material as the light barrier 130.

In some implementations, one or more surfaces of the emission chamber102 are coated with an optical filter, a partially-reflective coating,an anti-reflective coating and/or an anti-scratch coating. For example,the emitter window 122A can include a coating 132, such as an opticalfilter coating, an anti-reflective coating and/or a non-transparentcoating (e.g., black chrome), disposed on its top or bottom side (or onboth sides). In some situations, both sides of the emitter window 122Ahave the same coating provided thereon. In other cases, the top andbottom sides of the emitter window 122A have different coatings.Further, in some instances, one or both sides may have two (or more)different coatings. The coating(s) may be partially reflective to somewavelengths of light (i.e., wavelength(s) that can be detected by thereference pixels). Thus, for example, some of the light reflected by theemitter window 122A can be incident on the reference pixels 128. In someimplementations, a passive optical element is mounted on, orincorporated into, the emitter window 122A. Examples of such a passiveoptical element include a reflective patch, a diffractive opticalelement, and/or a refractive optical element such as a prism.

Instead of, or in addition to, providing a partially reflective coatingon a surface of the emitter window 122A, a reflective coating 133 can beprovided on the surface of the light barrier 130 or the non-transmissiveregion 131 of the optics member 116. Such a reflective coating can helpdirect some of the emitter light toward the reference pixels 128.

When light from the emitter 106 is reflected by the emitter window 122Aor other surface of the emission chamber 102 toward the reference pixels128, such light preferably is not incident on the detection pixels 124.In some cases, such as the implementation of FIG. 2, the light barrier130 helps prevent light reflected by the emitter window 122A from beingincident on the detection pixels 124.

Although the light barrier 130 can help reduce optical cross-talkbetween the detection pixels 124 and the reference pixels 128,incorporating the light barrier into the module 100 may increase theoverall footprint and/or height of the module. Thus, in some instances,it may be desirable to provide the advantages of using reference pixels128 without the need for the light barrier 130. In such cases, othertechniques can be used to address the issue of optical cross-talk.Examples of these other techniques are described below and can be usedtogether with, or instead of, the light barrier 130.

In the implementation of FIG. 2, the detection pixels 124 may have arelatively broad field of view (FOV) such that they sense incoming lightfrom a broad angle. In some instances (e.g., in a module without thelight barrier 130), it can be advantageous to narrow the FOV of thedetection pixels 124 to reduce the amount of optical cross-talk sensedby the pixels 124. This can be achieved, for example, by providing oneor more micro lenses 140 over the detection pixels 124 (sec FIG. 3).

In some instances, a micro lens 140A also can be placed over thereference pixels 128. By displacing the micro lens 140A slightly in thedirection of the emitter 106, the reference pixels 128 can collect morelight from the emitter. Such an arrangement also can help reduce theamount of optical cross-talk sensed by the reference pixels 128. In someimplementations, the micro lens over the reference pixels is omitted.

In some cases, providing micro lenses 140 to narrow the FOV of thedetection pixels 124 can obviate the need for a light barrier 130 (seeFIG. 2) to prevent light reflected by the emitter window 122A from beingincident on the detection pixels 124. In implementations that do notinclude the light barrier 130, the section 131 of the optics member 116that substantially attenuates or is non-transparent to light emitted bythe emitter 106 also can be omitted such that the transmissive widows122A, 122B are not separated from one another by an opaque ornon-transparent section 131. Eliminating the need for the light barrier130 can help reduce the overall size of the module, which can beadvantageous for applications in which the module is to be integratedinto a handheld device such as a smart phone or tablet in which space isat a premium.

In some implementations, stacks 144 can be provided as shields aroundone or more of the pixels 124, 128 (see FIG. 4). The stacks 144, whichcan be composed, for example, of metal or other layers, can help definethe FOV for the detection pixels 124 and can help reduce opticalcross-talk caused by emitter light reflected toward the detectionpixels. Likewise, the stack 144 around the reference pixels 128 can helpensure that light reflected by the emitter window 122A is incident onthe reference pixels, but that light reflected by an object outside themodule is not incident on the reference pixels. A respective stack 144can partially, or completely, surround each individual pixel 124, 128laterally. Further, the stacks 144 can be provided instead of, or inaddition to, the micro lenses 140, 142 of FIG. 3.

In some instances, as illustrated in FIG. 5, the sensor chip 108 can beembedded within layers of the PCB 110. Such an arrangement canfacilitate optical separation of the reference pixels 128 from theactive detection pixels 124, thereby reducing optical cross-talk.Further, one or more layers 110A of the PCB stack 110 itself can be usedto provide optical separation between the reference and detectionpixels. By embedding the sensor chip 108 within the PCB 110, design ofthe light barrier can be made easier because considerations related tomaterial and mechanical stress tend to be less important in view of theinherent protection of the sensor 108 by the PCB 110. Further, by usinglayers 110A of the PCB 110 to provide the optical separation, theoverall height of the module can be kept relatively small.

In the foregoing examples (including the example of FIG. 5), a singlesensor chip 108 includes both the active detection pixels 124 and thereference pixels 128 (as well as the control logic, decoder logic andread-out logic). In other implementations, the reference pixels 128 areintegrated into a chip 108A separate from the chip 108B containing theactive detection pixels 124 (see FIG. 6). Each of the chips 108A, 108B,which can be embedded within the PCB 110, also can include appropriatecontrol logic, decoder logic and/or read-out logic. Embedding the sensorchip(s) within the PCB layers can be combined, for example, with othertechniques described here (e.g., a partially reflective or other coatingon a surface of the emission chamber; the addition of micro lenses 140,142 over the pixels; the addition of reflective layers 144 around thepixels).

In some instances, in addition to embedding the sensor chip(s) 108A,108B in the PCB 110, the emitter chip 106 also can be embedded with thePCB layers (see FIG. 7).

Embedding the sensor and/or emitter chips 108, 106 within the PCB 110can achieve other advantages in some instances. For example, the needfor bonding wires can be obviated. Eliminating the need for bondingwires, which tend to be vulnerable to mechanical vibrations, can beuseful. Further, bonding wires introduce parasitic capacitances andinductances, which make high frequency applications more challenging.Thus, eliminating the need for bonding wires can facilitate highfrequency applications.

Embedding the sensor and/or emitter chips 108, 106 within the PCB 110also can help protect the chips better in some implementations becauseonly the passivated chip surfaces of the chips are exposed.

In some implementations, the active detection pixels 124 and thereference pixels 128 may have integration times (i.e., exposure times)that occur simultaneously. However, in other cases, the module can usemultiple non-overlapping integration times (e.g., one for the activedetection pixels 124 and another for the reference pixels 128). Anexample of the timing for such an implementation is illustrated in FIG.8A. In some cases, a variable integration period 152 can be used for theactive detection pixels 124, whereas a fixed integration period 154 canbe used for the reference pixels 128. The exposure time for thedetection pixels 124 can be adjusted, for example, to reduce thesignal-to-noise (S/N) ratio based on the level of signals reflected byobjects in the scene 26. The active pixels 124 can be read out, forexample, during a first period 156, and the reference pixels 128 can beread out during a second period 158. The duration of the read out timemay be a function, for example, of the pixel(s) size.

In some implementations, the sensor's control circuitry is configured totune the integration times of the reference pixels so as achieve anaffective sensitivity for the pixels. Varying the integration times forthe reference pixels can provide an alternative to varying the aperturesize of the pixels. For example, a longer integration period maycorrespond to pixel having a relatively large aperture, whereas asmaller integration period may correspond to a pixel having a relativelysmall aperture. In some cases, tunable integration times can be used toinitiate (or end) the reference pixel integration period at a specifiedtime relative to the integration period of the active detection pixels.FIGS. 8B-8C illustrates examples that can be achieved using tunableintegration times for the reference pixels. As illustrated in theexample of FIG. 8B, the reference pixel integration 162 occurs duringthe middle of the active pixel integration 164. In contrast, as shown inthe example of FIG. 8C, the reference pixel integration occurs for shortperiods 166, 168 at the beginning and at the end of the active pixelintegration period 164, which can result in averaging of the thermalphase shift of the emitter 106 that occurs over time. In some instances,a particular reference pixel is integrated during both integrationperiods 166, 168. In other cases, a first reference pixel may beintegrated during the first integration period 166, and a differentsecond pixel may be integrated during the second integration period 168.

In some cases, such as where the sensor 108 has multiple referencepixels 128, the sensor's control circuitry can control the referencepixels such that different pixels have integration periods of differentduration. FIG. 8D illustrates an example, in which a first referencepixel (or subset of reference pixels) integrates during a firstintegration period 172 having a first duration, a second reference pixel(or subset of reference pixels) integrates during a second integrationperiod 174 having a second duration longer than the first integrationperiod, and a third reference pixel (or subset of reference pixels)integrates during a third integration period 176 having a third durationlonger than the second integration period. In the illustrated example,each of the pixels is integrated at a time near the middle of theintegration period for the active pixels, although this need not be thecase for all implementations. Further, each of the integration periods172, 174, 176 is shorter than the integration period 164 for the activepixels.

The dynamic range of the sensor depends on the maximum amount of chargethat each pixel can accumulate. Thus, for some implementations, thedynamic range of the sensor can be increased by increasing the maximumcharge capability of the reference pixels 128.

In the foregoing examples, various techniques are described to helpisolate the detection pixels 124 and reference pixels 128 optically fromone another so as to reduce optical cross-talk (i.e., to reduce theamount of light reflected, for example, by the emission window 122A thatis sensed by the detection pixels 124, and to reduce the amount of lightreflected by an object in the scene 26 that is sensed by the referencepixels 128). Nevertheless, as described below, in some implementations,even when such optical cross-talk is present, it is possible todetermine the phase difference, and thus the distance to an object inthe scene.

For example, based on prior calibrations of the imaging system, it canbe determined that a particular detection pixel 124 has a firstsensitivity a defined as the ratio of two sensed signals (Aref/Bref)each of which results from light reflected by the emission window 122A(or other surface of the emission chamber) (FIG. 9, block 200). In thiscase, Aref represents the component of light sensed by the detectionpixel 124 resulting from light reflected by the emission window 122A (orother surface of the emission channel), and Bref represents thecomponent of light sensed by a particular reference pixel 128 resultingfrom the light reflected by the emission window 122A (or other surfaceof the emission channel). Likewise, based on prior calibrations of theimaging system, it can be determined that the reference pixel 128 has asecond sensitivity 13 defined as the ratio of two sensed signals(Aobj/Bobj) each of which results from light reflected by an object inthe scene 26. In this case, Aobj represents the component of lightsensed by the reference pixel 128 resulting from light reflected by theobject in the scene 26, and Bobj represents the component of lightsensed by the detection pixel 124 resulting from light reflected by theobject in the scene. In general, each of α and β will have respectivevalues between 0 and 1, and typically should have values closer to 0.Thus, the sensitivities α and β represent indications of the opticalcross-talk that occurs between the reference and active detectionpixels. The values for α and β can be stored by logic or memory in theimaging system (FIG. 9, block 202).

In the following discussion, it is assumed that the two pixels (i.e.,the detection pixel and the reference pixel) have differentsensitivities from one another (i.e., that a and (are different).Signals sensed by each of the two pixels are measured and read out toobtain a reference vector {right arrow over (R_(ref))} and an objectvector {right arrow over (R_(obj))}, respectively (see FIG. 9, block204; FIG. 10). Each of these vectors represents the total amount oflight detected, respectively, by the reference pixel 128 or thedetection pixel 124, and thus each vector represents the sum of the twosignal components sensed by the particular pixel (i.e., a firstcomponent of light sensed by the pixel resulting from the lightreflected by the emission window 122A (or other surface of the emissionchamber) and a second component of light sensed by the same pixelresulting from light reflected by an object in the scene 26). Althoughthe two signal components are superposed on one another, the phase φ,and thus the distance to the actual object in the scene, can becalculated by the sensor's processing logic as follows:φ=phase({right arrow over (obj)}/{right arrow over (ref)}),where:{right arrow over (obj)}=({right arrow over (R _(obj))}−α×{right arrowover (R _(ref))})/(1−α×β){right arrow over (ref)}=({right arrow over (R _(ref))}−β×{right arrowover (R _(obj))})/(1−α×β)(See FIG. 9, block 206) To obtain advantageous use of the foregoingtechnique for determining the phase difference, the sensitivities α andβ for the various pixels should be substantially independent of theenvironment in which the sensor module is located.

FIG. 11 illustrates a portion of an optoelectronic module that has asensor including reference pixels 128. In this example, the opticsmember 116 includes a transmissive cover (e.g., a cover glass) 122 abovethe PCB substrate 110. Both sides of the cover glass 122 are coated, forexample, with optical filters 121A and 121B, respectively. The opticalfilters 121A and 121B can filter a particular wavelength or range ofwavelengths of light emitted by the emitter 106. Further the opticalfilters 121A, 121B are coated, for example, with black chrome 184A, 184Bto prevent cross-talk via the cover glass 122. Respective parts of thefilters 121A, 121B are not covered with the black chrome so as to definea transmissive window 122C that allows light from the emitter 106 topass out of the module. The presence of the black chrome coating 184B onthe sensor-side of the optics member 116 also can help enhance theamount of light that reflects from the optical filter 121B toward thereference pixels 128. In some cases, to reduce the likelihood that toomuch emitter light is reflected by the black chrome layer 184B onto thereference pixels 128, the black chrome layer 184B can be provided as apattern 185B with openings (e.g., dots, lines, concentric circles) so asto reduce the amount of light incident on the reference pixels 128.Further, the black chrome layer 184A can be provided as a pattern 185Awith openings (e.g. dots, lines, concentric circles) so as to reduce theamount of light incident on the reference pixels 128. As illustrated inthe example of FIG. 11, the patterns 185A, 185B include openings 186A,186B where there is no black chrome. Thus, while the presence of theblack chrome coating 184A, 184B can enhance the amount of lightreflected to the reference pixels 128, providing part of the blackchrome coating as a pattern 185A, 185B can be used to prevent too muchlight from being incident on the reference pixels 128. In someimplementations, the black chrome layers 184A, 184B need not be providedas patterns 185A, 185B with openings. For example, the chrome layers184A, 1854 may be provided as a single opening such as a circle, squareor other geometric shape.

Use of the features and techniques in the foregoing implementations canresult, in some instances, in small sensor modules (i.e., having a smallheight and/or a small footprint). Further, the foregoing implementationscan help reduce or eliminate optical cross-talk. Such small modules canbe integrated advantageously into devices such as smart phones, tablets,and other host devices in which space is at a premium.

Various modifications can be made to the foregoing examples. Further,features from the different examples can, in some instances, beintegrated in the same module. Other implementations are within thescope of the claims.

What is claimed is:
 1. An optoelectronic module comprising: anillumination source; a sensor including spatially distributed detectionpixels and at least one reference pixel; an optics member disposed overthe illumination source and the sensor, the optics member having a firsttransmissive region over the illumination source and a secondtransmissive region over the detection pixels; a light barrierseparating an emission chamber of the module from a detection chamber ofthe module, wherein the illumination source and the at least onereference pixel are in the emission chamber, and wherein the detectionpixels are in the detection chamber; and a partially reflective coatingon a surface of the first transmissive region over the illuminationsource wherein the coating is partially reflective with respect to awavelength detectable by the reference pixel and is arranged such thatsome light from the illumination source is reflected by the coatingtoward the at least one reference pixel.
 2. The optoelectronic module ofclaim 1 including a partially reflective coating on a surface of thefirst transmissive region facing the illumination source.
 3. Theoptoelectronic module of claim 1 including a partially reflectivecoating on a surface of the first transmissive region facing away fromthe illumination source.
 4. The optoelectronic module of claim 1including a partially reflective coating on each of opposite surfaces ofthe first transmissive region.
 5. The optoelectronic module of claim 1including a reflective coating on a surface of the light barrier facingthe illumination source.
 6. The optoelectronic module of claim 1 whereinthe optics member includes a non-transmissive region separating thefirst and second transmissive regions, the non-transmissive regionhaving a reflective coating on a surface facing the illumination sourceand arranged such that some light from the illumination source isreflected by the reflective coating toward the at least one referencepixel.
 7. An optoelectronic module comprising: an illumination source; asensor including spatially distributed detection pixels and at least onereference pixel; an optics member disposed over the illumination sourceand the sensor, the optics member having a first transmissive regionover the illumination source and a second transmissive region over thedetection pixels, wherein the first transmissive region has a firstcoating on a first surface facing the illumination source and a secondcoating on a second surface facing away from the illumination source; alight barrier separating an emission chamber of the module from adetection chamber of the module, wherein the illumination source and theat least one reference pixel are in the emission chamber, and whereinthe detection pixels are in the detection chamber; and wherein each ofthe coatings is at least one of an optical filter coating, apartially-reflective coating, an anti-reflective coating or anon-transmissive coating.
 8. The optoelectronic module of claim 7wherein at least one the first or second coating comprises black chrome.9. The optoelectronic module of claim 7 including a respective blackchrome coating on each of opposite surfaces of the first transmissiveregion.
 10. The optoelectronic module of claim 7 wherein each of the oneof more surfaces of the first transmissive region has a black chromecoating and an optical filter coating thereon.
 11. The optoelectronicmodule of claim 7 further including a passive optical element mountedon, or incorporated into, the first transmissive window.
 12. Theoptoelectronic module of claim 11 wherein the passive optical elementincludes at least one of a reflective patch, a diffractive opticalelement, or a refractive optical element.